Mercury cathode discharge tube



Feb. 20, l940. M. J. DRUYvsTEYNfl-:T AL 2,191,249

IMERCURY CATHODE DISCHARGE TUBE Filed April l5, 1958 o Patented Feb. 20, 1940 UNITED` STATES 2,191,249 o ,y MERCURY oA'rHonE DISCHARGE 'rune Mari Johan Druyvesteyn and Tom Jurriaanse, `Eindhoven, Netherlands, assignors to N. V.

Philips Gloeilampenfabrieken,

r Netherlands Eindhoven,

Application April 15, 1938, Serial No. 202,332

In Germany April 10, 1937 s claims. (c1. 25o- 275) Our invention relates to mercury-cathode current-converting tubes, and particularly to tubes in which an auxiliary anode arranged within a screen in the neighbourhood ofthe cathode mercury serves to maintain a cathode spot, and an ignition control anode arranged outside the screen serves to control the mean value of the converted current` Y It is known to separate an auxiliary discharge from the discharge chamber proper by means of' a screen, and use an auxiliary anode to cause this discharge toemerge from the screenand ignite the main discharge. For this purpose a voltage, `which is positive with respect to the cathode, is applied atthe proper moment of the alternating current cycleto an auxiliary anode arranged outside the screen. This anode causes the ignition of the main discharge at the cathode spot of the auxiliary discharge through a narrow slit provided between the screen and the level of the mercury.

- Such a construction, however, has the drawback that the cathode spot of the auxiliary discharge moves tov and fro inside the screen, and

continuously changes its position with respect to the auxiliary anode which is located outside said screen. As a result the electrostatic condi- V tions between the auxiliary anode and the cathode spot vary and cause irregular operation of the control device. Furthermore, difculties `are caused by the narrow slit which is present between the screen and the mercury. More particularly, due to the varying conditions of condensation, the height of the mercury level varies continuously and at a low mercury level a slit adapted to the highest mercury level acquires such a widththat there is danger of premature ignition of the main discharge. At the lowest anode voltages the lines of force starting from the auxiliarymanode and from the main anode itself will penetrate into the interior of the screen so that a delay in the establishment of the discharge can no longer be obtained.

The main object of our invention is to overcome 5 the above drawbacks, and for this purpose we provide an anchoring body within a screen whose interior is accessible to the outer discharge chamber only through an opening provided immediately above the mercury, so that the inner and outer mercury surface are connected together without interruption, and arrange anignition control anode outside this screen and in the neighborhood of the opening in such manner 55 that the electrostatic lines of force starting therefrom pass through the opening to the interior of the screen, along a very short path. r

With such a construction the cathode spot of the auxiliary discharge is always located `at the same point,. and excessive vaporization and 5 movement o-f the cathode mercury is avoided. We have found that after the ignition, a cathode spot is generally formed outside the screen `so that the control has to be considered as an on the degree to which the lines of force from 2Q the anode areable to penetrate through the controlling member, and, consequently, on the anode voltage applied. On the contrary, in the present invention the ignition control anode directly in- `fluences the auxiliary discharge toy a much higher 25 degree than the main `anode does, so that the process is materially independent of the main anode voltage present at the moment. ThusA the construction should besuch that, even at the` highest voltages that may occur, the main anode 30 is incapable of ignitingat the screened cathode spot. The ignition control anode, however,

"should exert such an influence in the interior of the screen that at the control voltage utilized, it is capable of establishing a discharge at the 35 anchoring body inside the screen. As this discharge is established at an electrode outside the screen the cathode spot will have the natural tendency to displace itself in the direction of the ignition control electrode i. e. outside the screen, 4Q thus enabling themain anode to establish the main discharge at the cathode spot, immediately after the discharge has been established at the control anode, or to take it over from the ignition control electrode irrespectively of the instantaneous value of the main anode voltage, provided only that it exceeds the minimum value required for the ignition of an arc.

This independence of the main anode voltage is one of the greatest advantages of the ignition 5o device` according to the invention, because the accuracy and reliability of the establishment of the discharge are much greater than can be obtained with known forms of construction. Furthermore, the ignition device is only slightly dependent` on Q5 The present invention differs from the `usual 1li` temperature, and its sensitiveness to harmful electrostatic or electromagnetic inluences is immaterial, and the consumption of energy by the `auxiliary discharge and thecontrol is very low.

To increase the reliability of the ignition process according to the invention, we prefer to form the outlet of the screen as a tunnel. In thisv manner it is possible to reduce any excessive iniiuence exerted by the main anode in the interior of the screen and therebyr fulfill the condition that the main anode can ignite without the aid of the ignition control anode at even the highest anode voltage that may occur in practice;

Particularly at very high anode voltages, We prefer to still further reducethe iniiuence exerted by the main anode on the auxiliary discharge without affecting the influence of the control anode. For this purpose we provide adjoining the tunnel-like covering, a second screen which contains the ignition control anode and which also has an opening provided immediately above the mercury level, in such manner ,that the passageway between the outer discharge chamber and the. 'chamber which contains the auxiliary anode leads exclusively through the screen containing the control anode. In order that the invention may be clearly understood and readily carried intoI effect, We shall describe the same in more detail with reference to the accompanying drawing', in which:

.Figure l is a schematic view of a rectiiying installation according to the invention, and comprisingv a Vmercury-cathode current-converting tube, sectionized along line I-I of Fig. 2,

Fig. 2 is a sectionized view of the tube of Fig. l taken along line 1li-II, and L Fig. 3 is a sectionized fractional view of the tube taken along the line III-III.

The tube shown in Fig. 1 has an envelope comprising a vitreous portion I which forms three tubular `projections I8, 28, and 33, and. isl

hermetically fused at 35 to a cup-shaped metal cathode vessel 2 containing a mercury-cathode 4. Secured in good heat-transferring relationship to the bottom of vessel 2, for instance with.

hard solder, is an annular-shaped cathode-spot anchoring member t, for instance of nickel. A

housing 3, secured to vessel 2 by a stud 33, which v also serves as a cathode terminal, forms a space through which a suitable cooling Vliquid is circulated. 4

Extending into mercury @l is 'a screen 8 of a metal such as molybdenum, or of a heat-resistant insulation material, such as steatite. As shown in Figs. l and 2, the screen il, which is form-ed of a side piece and two removable covers 9 and HJ, extends over the end of the member 5 and forms two end chambers t and 'I connected by a passageway t@ (see Fig. 3). The interior of the screen 8 is connected to the main discharge space of the tube only through an opening i! formed between the end of the screen, the inner surface of member5, and the surfaceof mercury Il.

It will be noted that theheights of opening Il and passageway 6@ are considerably greater than their widths, in order that variations in the level of the mercury will only slightly change the area of this opening. In the same manner, passageway Sil is .defined by the top and side of screen 8, the surface of mercury "i, andthe inner surface of member 5.

As shown member il extends into the main discharge space of the tube, which enables the cathode spot to move smoothly at each new `ignition along they inner side of the.r anchoring member 5 into the outer discharge chamber.

Without this measure the lcathode spot would emerge more or less in jerks due to its breaking voil* from the anchoring member.

from a metal disc I9, for instance of ierrochromium, h-ermetically fused into the vitreous projection it and carrying a terminal it. A spring I6 serves to place plunger I5 in the position shown andto carry current thereto, anda coil 2| surrounding projecting portion I8 serves to lift plunger I5 and thus to raise anode I2 from the mercury. v f

Within chamber l and adjacent to passageway 6U, an ignition control anodeV it is-disposed lat-y erally from the discharge path connecting the passageway 30 and the outer discharge space.

, The ignition control anode I3 is supported from the lower end of a metal rod 25 whose upper end is secured to a metal disc 2l, for instance of ferrochromium, hermetically sealed in the vitreous projection portion 23 and carrying a terminal 5. kRod 25 is guided and protected from the discharge byaporcelain tube 2t. It will be noted that tubes 2t and 2t also` serve to hold screen 8 in position and for this purpose, the covers 9 and It are clamped thereto.

Coaxially arranged within the central portion of the envelope is a Vmainlanode 29 in the form of a graphite cylinder in which two vertical grooves are provided to take tubes 2li and 26. Anode 29 is supported from the lower end .of a metal rod 30 whose upper end is secured to a disc 3 2, for instance of ferrochromium, hermetically sealed in the-top of projection 33 and provided with a terminal 52. A protective tube 3l Vof insulating material, such as ,porcelairu` surrounds rod 30 and extends into anode 29 to .protect the junction point between rod SI) and anode 29.

Supported from tube SI and supporting tubes .20 n

and 26 is a cylindrical screen of sheet metal which isclosed at the top and serves to prevent 29'i's connected to rterminal 53 of a load 36 whose other terminal 54 is connected to terminal 55 of an A. C. supply. The other terminal .6I of the A. C. supply is connected to cathode terminal 33 to complete the rectifying circuit.v

Terminal Idl of ignition anode E2 is connected through coil 2|, a iixed resistance 22, and a singlethrow switch 23 to the positive terminal of a D. C. supply 2d, whose negative terminal is connected to cathode terminal 38; Upon closure of switch 23, coil ESI is energized and lifts anode I2 from the mercury to thereby initiate an auxiliary discharge of about 2 amperes. For this purpose D. C. supply 24 should be of aboutr 70 l volts.

Connected across D; C. supply 2d is a poten- "fr tiometer 42 having a sliding contact 5t connected through a conductor 5l' to a contact l of a rotary contact-maker A having a second Contact 58 connected to terminal 5I'of the control anode I3. Fixed contacts `lll andA 58 are periodically 7,5

i side the chamber S `a main cathode-spot which" connected by a rotary contact drivenby a synchronous motor 39 energized from-then. C. supply. For a purpose later tobe referred to,

contacts 4I and `58 are mounted ona ring 59 of insulating material adapted to be rotated as `indicated by the double-headed arrow. i

`ertedby the. latter in chamber li is insuihcient to produce thisresult. However,. when contactmaker A is placed in operation, a new discharge `is set up in chamber 'I and this, in turn initiates a discharge between ignition control anode I3 and the auxiliary discharge always present within chamber 6. This new discharge produces outcauses ignition of the main discharge, l I

The mean value of the rectified current flowing through load 36 can easily be'adjusted by altering the angular position of the contacts 4I and 58 of contact-maker A, which `displaces `the timing of the D. C. impulses at electrode I3 with respect to each cycle of the A. C. voltage applied to main anode 29, so that the mean value of the rectified current through load 36 is altered. Although this control is in eiectequvalent to the action of a control grid, it is not `dependent on the voltage l as is characteristic for thelatter one. i

It will be noted that the back ignition security of the tube may be conveniently increased by applying to the ignition control anode I3 during the blocking phase a potential which impedes the ignition of the discharge in the blocking direction, i. e. by applying a potential which is negative with respect to the cathode,

converting tube because the continuous ionization of the gas filling by the auxiliary discharge remains restricted to chamber 6 so' thatthe sei curity against back ignition exceeds to an appreciable extent that of a single-phase tube having an open auxiliary discharge and one of the usual control grids.

Although we have described our invention in connection with specic examples and applications, We do not wish to be limited thereto but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What We claim is: f

1. A current-converting tube comprising an envelope, an anode, a mercury cathode spaced from said anode to form a main discharge space, screening means `forming at the surface of the `mercury cathode a chamber connected to thel main discharge space by anopening adjacent the surface of the mercury, means to maintain a cathode-spot including an auxiliary anode within said chamber," a cathode-spot anchoring "2. A current-converting tube comprising Aan envelope, a main anode,` a mercury `cathode spaced `from saidanode to form a main ldischarge space," screening means formed at the -Y surface of the mercury cathode, a chamber connected to the main discharge space through an opening, thelsurface` `of the mercury cathode forming theilower boundary of said chamberand opening, means to maintain a cathode spot including `an auxiliary anode within` said'chamber and a cathode-spot anchoring member'partly immersed in saidmercury cathode, and means to control the mean value of the converted current including an ignition electrode disposed outside said `.chamber and laterally from the discharge i path between said opening andsaid `main anode, said cathode-spot anchoring member extending from `withi`n.said screening means through the opening to the main discharge space of the tube i and forming `with `the mercury cathode a continuous anchoring line passing through. said opening in the direction of saidzignitiori'controlelec-v trode,` the influence upon the starting of the main4 discharge of thel electrostatic lines of `force from the main anode andfrom theignition control electrode being such that `ignition of the main discharge from the auxiliary dischargepisV charge space, screening means forming atathe surface of `themercurycathodea chamber connected to` the `main discharge space 'by` a passageway adjacent the `surface of the mercury, means to maintain a cathode-spot including an auxiliary anode Within saidchamber, a cathode-spot anchoring member partly within the chamber, and meansto-'control the mean value of the converted current including an ignition control electrode disposed near said opening but laterally from the discharge path connectingzsaid opening `and said main anode so that the electrostatic x lines of force starting from said ignition control electrode pass through theopening and into the chamber. i

4. A current-converting tube comprising an envelope, a mainl anode, a mercury cathode spaced from said anode to form a main discharge space, an elongated cathode-spot anchoring i member partly immersed in said mercury, screening means enclosing a portion of `said member including an ignition control electrode within `said second chamber and adjacent said opening,

said control electrode being disposed laterally from the discharge path connecting said opening and said main anode so that the electrostatic lines of force starting from said `ignition control electrode pass through said opening and `into said iirst chamber. i

5. Av current-converting tube comprising an envelope, va main anode, a mercury cathode spaced from said anode to form a. main discharge space, screening means forming at the surface of the mercury cathode a chamber connected to the main discharge space by an opening adjacent `the surface of the mercury, means to maintain A a cathode-spot including. an` auxiliary anode Withinn said chamber, a cathode-spot anchoring member Within the chamber and' extending intoA connecting saidopening and said main anode v` vso that the electrostatic'linesof force starting from said ignition control electrode pass through the opening and into `the chambersl f e v '6. A current-converting tube comprisingl an envelope, a main anode, a mercury cathode spaced from said anode to form a main discharge space, lscreening means forming a chamber at the surface of the mercury cathode, a cathode-spot anchoring member vpartly Within the` chamber and forming with ysaid screening means an. opening adj acentthe mercurysurface and connecting saidchamb'erand main discharge space, means to maintainy a cathode-spot including lan auxiliary anode within said chamber, and means to control themean value ofthe converted current including an ignition control electrode disposed near said .opening butdaterally from the discharge path connecting said opening and said main anode so that the. electrostatic lines of force starting from said ignition con-trol' yelectrode pass through the opening and into the chamber. 1

7. A current-converting tube comprising anenvelope, an anode, a mercury cathode spaced from `said'anod'e to form Va main discharge space,

screening means forming at the surface of the s mercury cathode a chamber havingr a tunnelshaped opening, means to maintain acathodespot includingan auxiliary anode Within said chamber, ay cathode-spot anchoring member partly Within `the chamber, a portion of said screening means forming a chamber connected to said opening and having a second opening adjacent the mercury surface and communicating with the main discharge space, said rstchamber communicating with the main discharge space only through said second chamber, and means to control the mean value ofthe converted current lincluding an ignition control electrode disposed- Withinv said second chamber.

3. A currenteconverting tube comprising an` envelope, an anode, a mercury cathode spaced from said anode tol form a main discharge space, screening meansforming at the surface of the mercury cathode a chamber connected to the main discharge space by a single opening, the

height of said opening being substantially greater opening but laterally fromr the discharge -patr connecting said opening and said main anode' sothat the electrostatic lines of force starting fromsaid ignition control electrode pass through the opening and into the chamber. l

MARIJOHAN DRUYVESTEYN. TOM JURRIAANSE. ,y 

